1. Field of the Invention
The present invention relates to an optical fiber, a method for manufacturing same and an optical transmission channel. Particularly, the present invention relates to an optical fiber used in optical communications of a long-haul large-capacity transmission system using wavelength division multiplexing (WDM) technology, an unrepeated submarine optical cable system or the like, a method for manufacturing same, and an optical fiber and an optical transmission channel used in the wavelength division multiplexing (WDM) optical transmission.
2. Related Art
Usually, a wavelength used of an optical transmission signal on a single-mode optical fiber (SMF) for optical transmission is often in the vicinity of 1,300 nm (1.3 μm) or 1,550 nm (1.55 μm), while a wavelength used for a WDM transmission optical fiber is 1,550 nm (1.55 μm) where transmission loss decreases.
Recent yeas have seen development of a WDM transmission system as well as growing demands for suppression of non-linearity and suppression of dispersion.
In such a situation, there ha been proposed for long-haul large-capacity transmission fibers, a dispersion managed transmission channel comprising a combination of an optical fiber 1 provided at the anterior portion having an increased effective area (Aeff), positive chromatic dispersion and a positive dispersion slope and an optical fiber 2 provided at the posterior portion having negative chromatic dispersion and a negative dispersion slope, as shown in FIG. 1, to achieve lower residual dispersion as a whole.
In addition, an optical fiber having increased effective area (Aeff) is also utilized in an unrepeated submarine optical cable system used for communication between near-sea islands so as to suppress non-linearity.
Known as a manufacturing method of these WDM transmission single-mode optical fibers are some compositing methods such as a VAD (Vapor-phase Axial Deposition) method, an OVD (Outside Vapor Deposition) method, an MCVD (Modified Chemical Vapor Deposition) method and a method of combination thereof.
Further, as a method for increasing transmission capacity in optical transmission by use of an optical fiber, attention is focused on WDM optical transmission. Accordingly, much consideration has been made on optical fibers used in the WDM optical transmission.
Known as an optical fiber usable in the WDM optical transmission are a single-mode optical fiber (SMF) having zero dispersion wavelength in the vicinity of 1.3 μm, a non-zero dispersion shifted optical fiber (NZDSF) having no zero dispersion wavelength in the used wavelength range and the like. However, in these optical fibers, there is a problem of non-linearity such as self-phase modulation (SPM) or cross-phase modulation (XPM).
In order to solve the problem of non-linearity for the optical fibers described above, there has developed an optical fiber having a chromatic dispersion that is sufficiently far from zero and an increased effective area (Aeff). The effective area is expressed by the equation (MFD)2×π×k/4, where k is a constant number. An example of such an optical fiber is disclosed in Proceedings of the 1999 IEICE Electronics Society Conference, C-3-76 and C-3-77.
Such an optical fiber as disclosed in the above-mentioned proceedings has a chromatic dispersion of more than 20 ps/nm/km. Because of this chromatic dispersion, the accumulated dispersion is increased, which makes the optical fiber unsuitable for long-haul WDM optical transmission.